If Fox or some other studio had pulled the Mandarin thing, I don't think as many people would be okay with it.

If FOX had pulled off with their Marvel properties what Marvel Studios has, I dont think that would be true. But alas, we live in a world where Galactus was a Space Tornado, X-Men 3 was a cluster****, the first Wolverine was disappointing (to put it mildly).

Those things get held against the studio, rightly or wrongly, and while First Class was a step in the right direction, it hasn't washed out the stain of past blunders. Hopefully though, the next Wolvie and X-Men movies will follow in the footsteps of First Class. Same with the FF reboot.